[squeak-dev] Printing standard output from PipeableOSProcess on the Transcript

David O'Toole deeteeoh1138 at gmail.com
Sat Jan 15 17:21:36 UTC 2022

I get this warning when trying to create an instance of

Perhaps this indicates a related issue?

On Sat, Jan 15, 2022 at 11:40 AM David O'Toole <deeteeoh1138 at gmail.com>

> Hi David, thanks for your help. I indeed have the following in my About
> Squeak dialog: AioPlugin VMConstruction-Plugins-AioPlugin-eem.22 (i)
> The Delay suggestion did not work. I notice that I can start a new Scheme
> job, and the standard output begins flowing again, without ever producing
> the remaining output from the previous run, even though the run completed
> successfully. So the output is getting lost somewhere.
> Should I be doing [schemeOutput atEnd] whileFalse: [ | output | output :=
> schemeOutput upToEnd ] ? That seemed to prevent output entirely.
> Thanks for the references to those other places I could look. I will
> endeavor to debug this.
> On Sat, Jan 15, 2022 at 10:53 AM David T. Lewis <lewis at mail.msen.com>
> wrote:
>> Hi David,
>> On Fri, Jan 14, 2022 at 10:03:46PM -0500, David O'Toole wrote:
>> > I forgot to include the output method. Adding "flush" seems to have
>> helped,
>> > but output still stops coming well before it is complete.
>> >
>> > On Fri, Jan 14, 2022 at 9:49 PM David O'Toole <deeteeoh1138 at gmail.com>
>> > wrote:
>> >
>> > > I have a question relating to PipeableOSProcess. I'm trying to read
>> the
>> > > standard output from the process and (optionally) print it to the
>> > > Transcript. Several large chunks consisting of dozens of lines are
>> > > produced, but then output halts always after a certain number of
>> characters
>> > > (stopping in the middle of a line) even though I can verify that the
>> Scheme
>> > > process completed its entire job successfully and should have
>> produced more
>> > > output. Am I setting up / accessing the PipeableOSProcess incorrectly
>> in my
>> > > snippet here? I would greatly appreciate any tips you might be able
>> to give
>> > > on my investigating this further. I am running Squeak 5.3 on Linux.
>> > >
>> A likely source of the problem relates to reading available data from
>> an OS pipe, particularly if a large amount of data is involved. When
>> you send #upToEnd to the reader, you will get all of the data that is
>> currently available in the pipe. Meanwhile, pipe itself may be waiting
>> for someone to read from it before it allows the process that is writing
>> to the pipe (the Scheme interpreter in this case) to complete the write.
>> The end result is that when you read upToEnd from a pipe, you may not
>> receive the entire chunk of data that is being written by Scheme, and
>> you may need to wait for a few milliseconds and do another read to
>> get the rest.
>> For purposes of debugging, try putting a short delay before the #upToEnd
>> (Delay forMilliseconds: 200). If that makes it work, it will confirm
>> my guess above.
>> A couple of related notes for your information:
>> Take a look at the #upToEndOfFile method, as compared to #upToEnd.
>> You will not be able to use it for your Scheme interpreter because
>> it would wait for the Scheme interpreter to close its end of the
>> pipe, which is not what you want for in interactive connection. But
>> it may clarify the issues of reading from a pipe.
>> Also look at class BufferedAsyncFileReadStream, which deals with
>> the issue by populating its buffer based on AIO events (data available
>> on the pipe) to minimize the need for polling loops to get data
>> from a pipe. This is how you are reading the pipe data, and depending
>> on whether you have the AIOPlugin in your VM, it may be falling back
>> on its polling loop instead of being event driven. This should still
>> work fine but it affects timing of the data available from the pipe.
>> Regarding the #flush, I'm not sure I understand what you are doing
>> in the #step method, but when you write to the external Scheme
>> process on pipeToInput you do want to flush it. That ensures that
>> your data gets pushed out to the OS pipe, and makes it available
>> for Scheme to read from its end of the pipe.
>> HTH,
>> Dave
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